Conventionally, voice communications have been a mainstream of the cellular mobile communications with data communications constituting only a small part thereof. The data communications taking place occasionally are handled at the same transmission rate as the voice communications. Recently, however, demand for high speed data communications has been sharply growing, highlighting a signal transmission method that carries out multiple communications at different transmission rates. Thus, not a few papers are published about this subject. For example, J. M. Harris and S. P. Kumar, “Scheduling to Meet Mixed Quality of Service Requirement in Wireless Networks”, MoMuc, 1996, studied voice (low speed) communications and a signal transmission scheme over reverse traffic channels handling a mixture of data and image (high speed) communications, and proposed a method that separated in advance the voice traffic channels from image traffic channels. Considering actual mobile data communication services, however, it is expected that leading usage patterns are such that mobile stations access databases connected to a fixed network to read data. Accordingly, a signal transmission method over forward traffic channels becomes important. In addition, as a mobile communication scheme from now on, a CDMA scheme is promising because of its high frequency efficiency. It is possible for the forward traffic channels in the CDMA to achieve, besides the scheduling of transmission timings, orthogonalization of spreading codes, precise transmission power control considering the transmission power of other communications, and the like. The forward channels, however, undergo only insufficient study although they differ greatly from the reverse channels.
As described above, the signal transmission method for carrying out simultaneous multiple communications at different transmission rates is not yet in the practical use in the conventional cellular mobile communications. Although some papers examined it, an efficient signal transmission method has not yet been studied which integrally considers in the mobile communications the transmission power over the forward channels, the number of traffic channels and the balance between the forward and reverse traffic. In particular, only insufficient studies have been achieved of the CDMA mobile communication scheme which is promising from now on.